sh: Allow use of GENERIC_IOMAP

The synopsys PCI cell used in the later STMicro chips requires code to
be run in order to do IO cycles, rather than just memory mapping the IO
space. Rather than extending the existing SH infrastructure to allow
this, use the GENERIC_IOMAP implmentation to save re-inventing the
wheel.

This set of changes allows the SH to be built with GENERIC_IOMAP
enabled, it just ifdef's out the functions provided by the GENERIC_IOMAP
implementation, and provides a few required missing functions.

Signed-off-by: David McKay <david.mckay@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>